This invention relates to an electromagnetic plunger pump, and more particularly it is concerned with an electromagnetic plunger pump of the reciprocating type having therein a means for preventing the flow passage in the pump from being blocked up with air bubbles.
Generally, such reciprocating type of electromagnetic plunger pump is small in the diameter of a delivery piston or in the cross-sectional area of a cylinder and short in the length of stroke. Accordingly, when the electromagnetic plunger pump is used to draw kerosene or light oil from a storage tank located below the pump to feed it under pressure to a gasoline type burner and spray it therein for ignition and subsequent burning, it is usually increased in the number of stroke per unit time to maintain the delivery amount and is made considerably smaller in the delivery volume in comparison with the size of a valve chamber. Such pump is so-called a pump of lower volume efficiency. The air contained in the fuel oil and the gas gasified from the flowing oil due to the pumping action merely repeat the expansion and compression thereof by the reciprocating motion of the delivery piston, thereby causing a vapour lock phenomenon which obstructs a pumping action comprising the suction and discharge of the fuel oil.
U.S. Pat. No. 3,877,841 and U.S. Pat. No. 4,021,152 disclose the electromagnetic plunger pumps of the type in which after adjusting the pressure by a pressure adjusting mechanism in the form of relief valve built in the pump, the excess liquid under pressure of the pump is returned to the side of the suction valve of the pump. Particularly, in U.S. pat. No. 4,021,152, the electromagnetic plunger pump is provided with a means for preventing a vapour lock phenomenon comprising a particular duct for returning the excess liquid under pressure due to the adjustment of pressure to the side of the suction valve to thereby convert the air bubbles into comminuted form and return to the suction side without stagnation of the air bubbles. However, if the air bubbles enter into the side of the suction valve of such pump from the pipe at the suction side, it will cause a vapour lock phenomenon and further the air bubbles will be circulated in the pump and not easily discharged from the pump, so that the decrease in the delivery force of the pump and the stoppage of the pumping action frequently produce troubles due to the discontinuation of the fuel oil in burners or combustion apparatuses.
This is mostly because the above-mentioned type of pump which is of so-called an internal circulation system can draw the oil only the amount equal to that discharged, and merely repeats the compression and expansion of the air bubbles from the pressure chamber defined by the piston and the cylinder toward the discharge opening, so that the discharge of the air bubbles requires considerably long time and for such a period of time, the feed of the fuel oil is discontinued with the result that the fire is extinguished.
It is therefore a main object of the invention to provide an electromagnetic plunger pump in which the air bubbles existing or produced in the suction pipe can be rapidly treated to prevent the discontinuation of discharge of the fuel oil from the delivery side of the pump.
It is another object of the invention to provide an electromagnetic plunger pump having a vent valve means which allows the air bubbles to pass therethrough at a relatively lower pressure but does not allow the liquid under pressure having a viscosity to pass therethrough.
It is a further object of the invention to provide an electromagnetic plunger pump in which the excess liquid under pressure from the pressure adjusting mechanism is returned to a tank on exceeding a predetermined pressure to thereby increase the sum of the discharge amount at the delivery side and the return amount, i.e. the suction amount from the suction side, so that a vapour lock phenomenon may be prevented.
According to one aspect of the invention, there is provided an electromagnetic plunger pump comprising a pump body, an electromagnetic coil, a plunger case arranged on the longitudinal axis of the electromagnetic coil, an electromagnetic plunger fitted in the plunger case for reciprocating motion by the alternating action of the magnetic attractive force produced by intermittent current flowing through the electromagnetic coil and the biasing force of springs, and a pressure adjusting mechanism in the form of a relief valve provided in the pump body and normally shutting off a passage leading to the delivery side of the pump from a pressure adjusting chamber, wherein said pressure adjusting mechanism is provided with a vent valve means which allows only the air bubbles set free from a liquid under pressure to pass therethrough and which shuts off the liquid under pressure having a viscosity, and a duct which opens in the pressure adjusting chamber and a return opening flow connected to the duct are provided in the pump body to discharge the air bubbles and the excess liquid under pressure from the pressure adjusting mechanism outwardly of the pump.